Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

SPHENE

Online Encyclopedia
Originally appearing in Volume V25, Page 647 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

SPHENE , a See also:

mineral consisting of See also:calcium titan-silicate, CaTiSiO5, crystallizing in the See also:monoclinic See also:system. The crystals vary considerably in See also:habit, but are generally thin and See also:wedge-shaped; hence the name sphene, from the See also:Greek a¢ v (a wedge), given by R. J. See also:Hauy in 18or. The earlier name titanite, given by M. H. See also:Klaproth in 1795, is also in See also:common use. Twinning on the ortho-pinacoid is not uncommon. The See also:colour is See also:green, yellow, See also:brown or See also:black, and the lustre resinous to adamantine; crystals are transparent to opaque. The hardness is 51, and the specific gravity 3.5. The refractive indices and the optic axial See also:angle vary considerably with the colour of the See also:light: the See also:dispersion of the optic axes is inclined, and the interference figure seen in convergent light between crossed nicols is very characteristic of the mineral. Sphene is sometimes cut as a See also:gem-See also:stone, though it is rather too soft to stand much See also:wear; owing to its high dispersive See also:power it gives brilliant flashes of prismatic See also:colours.

As small embedded crystals, sphene has a wide See also:

distribution as an See also:accessory constituent of many kinds of igneous rocks (See also:granite, See also:syenite, See also:trachyte, See also:phonolite, &c.), and also of See also:gneiss, schist and crystalline See also:limestone. Sharply-See also:developed, transparent, See also:pale green crystals are frequently associated with adularia, See also:asbestos and See also:quartz in the crystal-lined crevices of the See also:schists of the Swiss and Tyrolese See also:Alps. Large, rough and dark-coloured crystals are found at See also:Arendal and KragerS in See also:Norway, and in granular limestone at See also:Diana in New See also:York and Eganville in See also:Ontario. A greyish, compact and impure' variety of spheric, known as " leucoxene," frequently occurs in basic igneous rocks as an alteration product of See also:ilmenite and See also:rutile. (L. J.

End of Article: SPHENE

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
SPHAERISTERIUM (Gr. ackaipear 1pun) 		[next]
SPHENODON, or TUATARA

Site © 2006 - Net Industries